Static and dynamic image reproduction at a remote location can be employed for both optical viewing and X-ray image reproduction for both static and dynamic objects. Reproduction of the brightness of an object is limited, however, by the dynamic range of the target of the pickup camera. When high contrast objects are in the field of view, the bright image points of the object lie as a rule in the dynamic range, while object points or regions of reduced brightness or radiation of reduced intensity can lie below the dynamic range.
In the present discussion, while reference may be made to "brightness" of an image, in accordance with the terminology used for optical image reduction, it should be understood that the term is employed also to refer to high intensity portions of an image field on the target as contrasted with low intensity portions in X-ray practice or of other image reproduction techniques.
The object points of reduced brightness generally are reproduced in the reproduced image of the object as image points of the same brightness. As a consequence, one cannot readily differentiate such object points of reduced brightness even though the brightness of these objects points may differ markedly, because of this levelling phenomenon. The structure of the so called "dark regions" of the object can generally not be ascertained in the reproduced image.
This limitation in the reproducibility of the appearance of the object in the image is by far one of the most important drawbacks of earlier pickup and reproduction techniques.
The problem is especially pronounced when the greatest possible degree of reproduction of the appearance of an object is desired, i.e. when practically total reproduction precision is desired.
For example, if this drawback is seen in light of X-ray technology and especially medical X-ray technology, it can be appreciated that the tendency to provide a uniform "dark region" corresponding to the portions of the object of the reduced radiation intensity, will reduce detrimentally the amount of information available as to the patient and is clinically a handicap.
It is possible to overcome this drawback by increasing the X-ray dose, but this approach places the patient, who must be exposed to the increased radiation dose at risk.